1. Field of the Invention
The present invention relates generally to image reproduction apparatus, and more particularly to an improved video-to-binary conversion circuit for use in such systems and which has the characteristic of compensating for the usual signal transformation errors that ultimately give rise to moire in the reproduced image when the original image sought to be reproduced is of the type formed by grouped arrays of dots, lines, holes, lights, etc.
2. Description of the Prior Art
One of the problems affecting the accuracy of reproduction in facsimile transmission/reproduction systems is that associated with the degradation of image which results due to the phenomena known as moire. The moire degradation is characterized by the occurrence of unintentional striations appearing in the reproduced image as a result of phase differences between the image-forming elements and the scan-sampling rate. Such striations are likely to occur in a reproduced image any time a periodic sampling is made of an image formed by a regular pattern of dots, lines, light sources or other image-forming elements. The facsimile reproduction of "half-tone" images is especially susceptible to such degradation.
Prior art attempts to solve the moire problem in facsimile reproduction systems have typically involved the judicious selection of either scan sample rate or scan sample element size which is most likely to cause the least amount of moire degradation. Such attempts have not however sought to deal directly with the problem and do not usually produce favorable results. Moreover, the prior art solutions have the effect of reducing the utility of certain facsimile transmission systems wherein a particular scan parameter must be preset, since no single setting is universally acceptable for all half-tone grids.